Call routing systems and information retrieval system are technologies which help users to identify and select one or more items from among a number of similar items. Call routing systems are commonly used by businesses which handle a large volume of incoming telephone calls. A conventional call routing system uses audio prompts to present a telephone caller with a choice of several selectable options (e.g., topics, people, or departments in an organization). The system then receives a request input by the caller as, for example, dual-tone multiple frequency (DTMF) tones from the caller's telephone handset, associates the caller's request with one of the options, and then routes the call according to the selected option. In a more “open-ended” call routing system, the caller may simply specify a person or other destination and is not limited to a specified set of options.
Information retrieval systems are commonly used on the World Wide Web, among other applications, to assist users in locating Web pages and other hypermedia content. In a conventional information retrieval system, a software-based search engine receives a text-based query input by a user at a computer, uses the query to search a database for documents which satisfy the query, and returns a list of relevant documents to the user. The user may then select one of the documents in the list to access that document.
Call routing and information retrieval systems can be enhanced by adding automatic speech recognition (ASR) to their capabilities. By using ASR, a user can simply speak his or her request or selection. A natural language speech recognition engine automatically recognizes the user's spoken request and outputs a text-based query, which is then used in essentially the same manner as in a more conventional call routing or information retrieval system. Among other advantages, adding ASR capability to call routing and information retrieval technologies saves time and provides convenience for the user. One problem with using ASR to augment these technologies, however, is the potential for introducing additional error from the ASR process, thus degrading system performance. In a conventional system (i.e., one which does not use ASR), the query is typically input in the form of text, DTMF tones, or some other format which is not particularly prone to error or ambiguity. In contrast, a spoken query may contain both grammatical and syntactical errors (e.g., skipped words, inversions, hesitations). Also, even the best natural language speech recognizers produce recognition errors. Consequently, an ASR-augmented call routing or information retrieval system is susceptible to recognition errors being propagated into the query, reducing the effectiveness of the resulting call routing or information retrieval operation.